Electrode



March 10, 1964 w. JUDA 3,124,520

I ELECTROCHEMICAL CONVERSION OF ELECTROLYTE SOLUTIONS Filed Sept. 28,1959 2 Sheets-Sheet 1 f FUEL "6' ELECTRODE 1 (NON FUEL OR OXYGEN 0R.OXYGEN- y 5s 2 ELECTROLYTE f2 ;5 SOLUTION 5 $4 ll '1 fi FUEL IONEXOHANGE QLECTRODE MEMBRANE v FUEL--MEMBRANE ELECTRODE 5-] BI-l l-- I I"-15 i 4 g i xi 6 g .65 a ,s i i ,3 2x495 l I 15201982502 WW 0.1m by AMM uiioflneg W. JUDA March 10, 1964 ELECTROCHEMICAL CONVERSION OFELECTROLYTE SOLUTIONS Fi led Sept. 28, 1959 2 Sheets-Sheet 2 UnitedStates Patent 3,124,520 ELECTRGCH-EMICAL CONVERSION OF ELECTRGLYTESQLUTEQNS Walter Linda, Lexington, Mass, assignor to Ionics,Incorporated, Cambridge, Mass, a corporation of Massachusetts FiledSept. 28, 1959, Ser. No. 842,892 12 Claims. (Cl. 204-8o) This inventionrelates to the electrochemical conversion, concentration, or dilution ofelectrolyte solutions by means of ion exchange membranes, and by DC.energy saved at least in part by direct conversion of combustiblegaseous or liquid fuels and/ or oxidant gases or liquids. Moreparticularly, the invention is concerned with electrolytic processes andthe cells used therefor wherein the electrolytic cell is equipped withat least one ion exchange membrane, one electrolyte solution, and atleast one porous fuel or oxidant-containing electrode. The processes ofthe present invention are also directed toward electrolytic proceduresinvolving the selective mi gration of ions across an ion exchangemembrane under the influence of a DC. potential.

Electrolytic cells comprising ion exchange membranes are well-known andare especially adapted for electrochemical conversions in which it isimportant to isolate one electrolyte solution. Many typical applicationsof ion exchange membranes in electrolysis or electrodialysis cells are,for example, described in Applications of Ion Exchange Membranes inElectrodialysis, by Mason and Juda, Chemical Engineering Progress, No.24, vol. 55, pp. 155-162 (1959). The D.C. electric energy required forelectrolysis and for electrodialysis is usually an important, economicfactor.

So-called fuel cells are well-known in which electrical energy (D.C.) isproduced from the chemical energy of oxidant and combustible gasesintroduced through appropriate porous electrodes. In the typical fuelcell, hydrogen gas, or other combustible gas, is introduced into a cellthrough a porous electrode made, for example, of a noble metal, or ofporous carbon containing a noble metal catalyst, or the like; andoxygen, or an oxygen containing gas, is introduced through a porouselectrode containing preferably an active metal oxide catalyst, the twoelectrodes being electrolytically connected through either an aqueouselectrolyte solution or a solid electrolyte, e.g. an ion exchangemembrane. In these cells, low voltage D.C. energy is produced directlyfrom the reaction of hydrogen and oxygen (or the like) including liquidfuels at conversion efficiencies considerably in excess of the usualconversion of chemical energy-to-heat-to-mechanical energy-to-electricenergy.

Obviously, fuel cells as well as any other source of DC. power can beused to supply the energy required for electrolytic conversion cells.

However, oxidant or combustible fuel electrodes, e.g. electrodesutilizing oxygen-containing gases or liquids or utilizing combustiblegases or liquids, or both, have not heretofore been incorporated withinelectrochemical conversion cells comprising ion exchange membranes.

It is an object of the present invention to provide a process involvingthe use of ion exchange membranes in combination with combustible and/oroxidant fuel electrodes. It is a further object of the invention toprovide means for electrolyzing or electrodialyzing solutions, wherein acell is employed containing at least one ion exchange membrane and atleast one combustible or oxidant fuel electrode, thereby providing meansto eliminate the energy required to discharge at least one gas at oneelectrode.

In general, the process and equipment of this invention utilizes atleast one ion exchange membrane defining at least one solutioncompartment and at least one combustible or oxidant fuel electrodewithin the same cell.

In one cell construction, according to this invention, a combustible oroxidant catalytic porous electrode is placed in face-to-face physicaland electrical contact with an ion exchange membrane (containing waterin sufficient quantity, for example in excess of 15%, to render the sameelectrolytically conducting). For convenience, combustible or oxidantcatalytic porous electrodes are hereinafter generically referred to asfuel electrodes. This combination fuel electrode-ion exchange membraneis called herein fuel-membrane electrode. In a fuel-membrane electrode,the membrane is a solid electrolyte which, among other functions,protects the very fine pores of the fuel electrode against capillaryadsorption of solution. Such adsorption interferes or prevents the fuelfrom interacting with the electrode. An electrolytic solution to bemodified electrochemically is then contacted with at least one suchfuel-membrane electrode in an electrolytic cell or in an electrodialysiscell. Alternately, a fuel electrode is contacted with an electrolytesolution which is separated from another electrolyte solution by an ionexchange membrane, the system fuel electrode/electrolyte solution/ ionexchange membrane/ electrolyte solution being incorporated in anelectrolysis or electrodialysis cell including another electrode whichcan be either a conventional electrode or another porous electrode.

Substantial savings in energy consumption of the electrolytic orelectrodialytic process are secured when a fuel electrode, andespecially a gas electrode, is integrated with the cells in which achemical conversion, concentration, or dilution takes place. In such acell, the necessity of supplying energy for the discharge of a gaseousproduct at the gas electrode is eliminated. Furthermore, by choosing agas electrode with an appropriate catalyst, the conversion of the gas toan aqueous ion can be accelerated sufficiently so that the gaseousreaction minimizes the DC. energy required under reasonable currents.Finally, comparing a conversion cell comprising fuel electrodes with aconventional conversion cell powered by a separate fuel cell, asignificant energy saving is obtained in the former because the ohmicloss of the separate fuel cell is eliminated.

The saving in total energy consumption obtained by eliminating theenergy required to discharge gaseous products at the electrodes isespecially significant where the voltage drops across the electrolytesolution and membrane (or membranes) is relatively small. Gaseousdischarge potentials, including overvoltages, often account for or moreof the total potential when electrolytic conversion cells are operatedat relatively high current densities, typically exceeding 10 amperes persquare foot, as is the case, for example, in single compartment cellsand in two compartment single membrane cells, with electrolyte solutionsof relatively high concentrations. The percentage of the total energyexpanded at the electrode decreases as the current density decreasesand/or as the number of ion exchange membranes and solution compartmentsincluded in the cell increases. Thus, in multi membrane cells, thesaving in DC. energy by the elimination of gaseous electrode products isrelatively less important than the production of electric energy in situby means of appropriate fuel electrodes.

Simple porous electrodes such as for example porous graphite can be usedin some cases to avoid the discharge of gases. In general, however, itis preferable that the fuel electrode is a porous conductor which iscapable of absorbing either the combustible gas or liquid or theoxygen-containing gas or oxidant liquid and which at the same timecomprises a suitable catalyst for the electrode reaction.

For hydrogen containing combustible gases, e.g., for the electrodereaction:

suitable catalysts include metals of group VIII of the periodic tablesuch as rhodium, platinum, palladium, and irridium. Other catalysts mayconstitute the electrodes themselves or they may be deposited on porousconducting structures including graphite, porous nickel and the like.Other combustile gases, including carbon monoxide and hydrocarbons,especially methane, in place of or in addition to hydrogen, can be used.Liquid combustible fuels, e.g., liquid hydrocarbons, methane, ethanol orthe like may also be used.

Oxygen-containing gases also require porous conducting electrodes inwhich it is especially important to provide a suitable catalyst. Porousconductors without catalytic activity, such as porous carbon (eg.graphite) can be used to convert oxygen to hydroxyl ion according to thereaction but their effectiveness is often inadequate. Reaction (2) isrendered efficient, by the incorporation of an appropriate catalyst intothe porous structure, especially at reasonably high current densitiesexceeding amperes per square foot. Porous carbon without catalyst issuitable for use in applications where relatively low current densitiesare desired. It can also be adequate, for example, for the suppressionof hydrogen evolution at a cathode. Preferably, however, the oxygenelectrode, e.g., the gas electrode at which an oxygen containing gas isconverted to the hydroxyl ion, comprises a conducting porous structureactivated with a metal oxide of catalytic activity for reaction (2),such electrodes including the oxides of silver, gold, iron, magnesium,cobalt, copper and others. In many cases the oxygen (or cathode porous)electrode may contain the metal capable of forming catalytically-activeoxides, and the oxide may be formed in situ by a preoxidation treatment.

Reference is also made to the many gas electrodes described in theliterature as part of fuel cells, including, for example, US. Patent No.2,913,511, US. Patent 2,860,175 and US. Patent 2,384,463 and GermanPatent 904,200 (1954), many of which are suitable for use according tothe present invention.

The use of fuel electrodes in electrolytic processes is of special valuewhen the electrolytic process is carried out in such a manner thatenergy requirement consists of relatively low D.C. voltage input and arelatively high current density. Evidently, their application is furtherenhanced when the source of hydrogen-containing and/ oroxygen-containing gas is readily avilable at low cost.

Combustible fuels include hydrogen and hydrocarbons such as methane,ethane, coal gas, etc., and also carbon monoxide and the like with thefuel anode. Oxidants include oxygen, air, halogens (gaseous or liquid),etc.

The efficiency of conversion of chemical to DO. electric energy at afuel electrode is highly dependent upon the nature of the electrolyte incontact with the fuel electrodes. For example, oxygen electrodes areespecially eflicient when the electrolyte is a caustic solution as theconversion proceeds from oxygen gas to hydroxyl ion. The reversiblevoltage of the reaction of oxygen gas to hydroxyl ion (reaction 2 above)in alkali is of the order of .1 to .2 of a volt, whereas in acid 1 voltis produced. Further, if an alkaline electrolyte contains significantquantities of other ions, the efiiciency of the energy production can beseriously impaired. For example, if an oxygen electrode containing asilver oxide catalyst is utilized in a mixed electrolyte of sodiumhydroxide and sodium chloride, the voltage (at reasonable currentdensities, e.g. exceeding 10 amps/ sq. ft.) is considerably less thanthat produced in a pure sodium hydroxide electrolyte, due to silverchloride formation. Oxygen electrodes tend to operate best in strongalkaline electrolytes containing a minimum of harmful contaminatinganions.

One important advantage of utilizing ion exchange membranes inelectrolytic cells comprising fuel electrodes is the flexibility givento the system by the membranes in that they permit the choice of theelectrolyte most suited for the particular fuel electrode. For example,an appropriate cation exchange membrane makes it possible to use a purecaustic solution in the compartment containing the oxygen electrodethereby obtaining the maximum potential from the oxygen/hydroxyl ionreaction; and to subject other electrolytes in the other compartments toelectrolysis or electrodialysis without contamination of either theelectrode or the solution to be converted.

1011 exchange membranes, both cation selective and anion selective,suitable for use according to this invention, have been described in theliterature. Reference is made, for example, to US. Patent Re. 24,865which de scribes a variety of membranes and a variety of processes fortheir preparation. In general, the membranes are solid polymericcross-linked electrolytes containing significant amounts of hydrationwater or gel water, preferably in excess of 15% of the weight of the dryresin in order to insure sufiicient conductivity of the membrane.

The first category of cells and processes of this invention utilizes afuel-membrane electrode, preferably a gas fuel membrane electrode, and aconventional electrode, the prime electrochemical product/ or productsbeing produced at the conventional electrode. Many electrochemicalprocesses of commercial significance using conventional chemicalconversion cells waste electric energy at one electrode. For example, inthe electro-winning of metals from their sulfate solutions, includingelectro- Winning of copper, zinc, nickel, cobalt, etc., oxygen isusually produced at an anode. The anode voltage which includes theoxygen discharge voltage as well as the oxygen overvoltage oftenrepresents a large fraction of the total electric energy required in thecell. The anode voltage can be between /3 and of the total cell voltage,depending upon the case. According to one embodiment of this invention,a gas membrane electrode is used as the anode and is supplied withhydrogen gas. In this manner, D.C. voltage requirements are lowered(rather than consumed in the discharge of oxygen). The membrane incontact with the hydrogen electrode protects the electrode againstcapillary sorption of the electrolyte solution (which causes loss ofcontact of hydrogen gas) and against ionic impurities.

If undesirable ions including, for example, nitrate ion in the case ofan anion membrane, or oxidizable cations such as ferrous iron in thecase of a cation membrane, are present in the electrolyte and afiect theproper functioning of the fuel electrode, then a second category ofcells and processes of this invention is advantageous, namely atwo-compartment cell comprising (1) a conventional electrode at whichthe prime product or products of the process are produced, (2) theelectrolyte solution from which the prime product or products areobtained by electrolysis, (3) an ion exchange membrane separating thiselectrolyte from (4) a second electrolyte adapted for use in conjunctionwith a fuel (preferably gas) electrode and (5) a fuel, preferably a gaselectrode in contact with the second electrolyte. Here it is importantthat the porous gas electrode be protected against the capillarysorption of the electrolyte by means of a treatment which renders thegas electrode repellent to the electrolyte solution without closing thepores. Such treatments are known to include, for example, the coating ofthe gas electrode with a thin film of paraffin or rubber or the like,without impeding gas flow through the electrode.

This second mode of operation is typically advantageous in applicationsWhere the electrolyte used as source of an electrochemical productcontains many impurities harmful to fuel electrodes. For example, ifcopper is to be plated from a sulfuric acid solution containing ferrousimpurities it is best to separate the impure electrolyte from a puresulfuric acid solution by means of a cation exchange membrane utilizinga hydrogen electrode as the anode, thereby continuously making hydrogenion at the anode, transferring hydrogen ion through the membrane andmaintaining the ferrous iron in the catholyte where it will not beoxidized.

For many applications, either the apparatus and mode of operation ofcategory 1 or that of category 2 can be used to advantage.

An important example is the use of an oxygen electrode incaustic-chlorine cells. The use of oxygen or air as a depolarizer bymeans of porous graphite cathodes in diaphragm cells has been describedpreviously. This method was ineffective in making a significantcontribution not only because of the absence of an appropriateoxygen-tohydroxyl ion catalyst in the graphite, but also because of thecharacter of the mixed electrolyte, NaOH-NaCl, obtained as catholyte inthe diaphragm cell. The usual oxide catalysts operate best, that is,give the highest voltage contribution according to reaction (2) in apure caustic solution, as pointed out above. Therefore, the use ofgraphite or, preferably, of a porous conducting oxygen or air electrodecontaining a catalyst is much more efiiciently carried out in acaustic-chloride cell which comprises a suitable cation exchangemembrane to separate the anolyte from the catholyte. In this way,substantially chloride-free caustic is produced at the cathode as iswellknown from US Patent Re. 24,865 and US. Patent No. 3,017,338, issuedJanuary 16, 1962. So long as the hydrogen normally produced at the usualsteel cathode is not salable, but merely lost to the atmosphere, it isvery advantageous to utilize an oxygen electrode such as describedabove, and supply said electrode with either oxygen or air, therebygaining about 1 volt out of 4 even at the commercially high currentdensities exceeding 100 amps/ sq. ft. A porous oxygen membraneelectrode, that is, an electrode having a porous oxygen conductor and acation membrane in face-to-face contact can also be used in the membranecell for caustic and chlorine.

A third category of cells and processes relates to the electrochemicalproduction of electrolytes in solution in whichotherwise two undesirablegaseous electrode byproducts are made. Typical of such applications arethe regeneration of spent pickle liquor for steel; and theelectrochemical conversion of sodium sulfate solution to sodiumhydroxide and sulfuric acid of interest, for exampie, to the rayonindustry.

Spent pickle liquor from steel contains sulfuric acid and ferroussulfate. Its disposal constitutes a major pollution problem. Aneconomical process which removes part or all of the iron and therebyrenders the sulfuric acid content effective again for pickling steelwould solve a major pollution problem. Electrolytic cells with ionexchange membranes can accomplish this purpose. One kind of such a cellutilizes a cation membrane separating the anode compartment from thecathode compartment. As anodes, lead or antimony-lead is a suitablematerial, whereas steel is a suitable cathode. Here the pickle liquor isfed to the anode, and the ferrous ion as well as. hydrogen ion aretransferred to the cathode compartment where the iron can becathodically precipitated as iron oxide or even deposited as metalliciron. The latter is undesirable because the build-up of iron isdifficult to remove from the cell. Alternately, an anion membrane may beused instead of the cation membrane and the pickle liquor may be fed tothe cathode compartment. Regeneration of the pickle liquor consists thenin the formation of iron-free sulfuric acid at the anode. In both cases,oxygen is evolved at the anode and hydrogen at the cathode. These twogases are not desired and the D.C. energy required for their releaseconstitutes the major portion of the energy for this recovery process ofspent pickle liquor. Here the use of a gas electrode, in particular ahydrogen electrode as the anode, constitutes a major saving in that thehydrogen-oxygen reaction in sulfuric acid can save from 2 to 3 volts ofthe total of 3 to 5 volts ordinarily required for the electrolysis ofpickle liquor. The hydrogen may either be supplied separately to aporous hydrogen anode and additional energy can be saved by supplyingoxygen or air to an oxygen electrode used as the cathode, or, if noinexpensive source of hydrogen is available, the hydrogen evolved at aconventional steel cathode can be fed to porous hydrogen anode, therebyrestituting the major portion of the energy wasted in the release of thehydrogen. In this manner, electric energy is primarily supplied only forthe selective transfer of the ions through the cation or anion membranerespectively and an important portion of energy previously wasted at theelectrode is now saved.

If low-cost hydrogen or other combustible gas is available at a steelmill, it may be advantageous to use it and at the same time preventevolution of hydrogen at the cathode by means of an oxygen or airelectrode. Here it is more efficient to utilize a second membrane in thecell permitting the use of a pure caustic catholyte in conjunction withthe oxygen electrode (see above). For example, such a cell wouldcomprise an oxygen or air cathode, a caustic catholyte, a first anionmembrane, a center compartment containing pickle liquor, a second anionmembrane, an anolyte of pure sulfuric acid and a hydrogen anode.Hydroxyl ion is produced at the cathode from oxygen and water,transferred through the first anion membrane into the pickle liquor,increasing its pH, sulfate ion is transferred from the centercompartment to the anolyte forming sulfuric acid by action of hydrogengas to hydrogen ion. The sulfuric acid anolyte is reused. Iron oxide isprecipitated from the center compartment.

Similar cells may be used to convert sodium sulfate in solution tocaustic and either to sulfuric acid or to sodium acid sulfate. Again,hydrogen is evolved at the cathode and oxygen at the anode. One way ofoperating such cells is to evolve hydrogen at a conventional cathode,such as are made of steel or Hastelloy, and to feed this hydrogen to ahydrogen electrode used as the anode, thereby preventing the evolutionof oxygen and regaining electric energy by reaction of hydrogen gas tohydrogen ion. If a source of combustible gas, hydrogen and/ or othergas, is economically available, then the use of an oxygen or airelectrode as the cathode is advantageous. In the latter event, theenergy produced from, for example, hydrogen and oxygen (or air) With twogas electrodes may be sufficient for the electrolytic decomposition ofsodium sulfate to sodium hydroxide and sulfuric acid, at reasonablecurrent densities in an appropriate low cell resistance, that is a celldissipating less ohmic energy than corresponds to the difference betweenabout 55 kilocalories per mol of water produced from H /2O minus about13 kilocalories per mol required to produce sulfuric acid and sodiumhydroxide from sodium sulfate.

In general, little D.C. electric energy is required in reactions inwhich both types of gaseous electrodes are used, providing that theenergy required for the electrochemical conversion is less than thatobtainable from the combined gas electrodes.

In order to better illustrate the invention of the present case,reference is made to the drawings wherein:

FIGURE 1 is a diagrammatic representation of a conversion cell adaptedfor chemical conversion of electrolytes having one compartment thereinand having at least one fuel-membrane electrode.

FIGURE 2 is a diagrammatic representation of a conversion cell havingtwo compartments, separated by an ion exchange membrane and at least oneelectrode may be operated as a fuel, preferably gas, electrode.

FIGURE 3 is a diagrammatic illustration of a cell with at least threecompartments defined by spaced ion exchange membranes therein having atleast one electrode as a fuel, preferably gas, electrode.

FIGURE 4 represents diagrammatically a variation and construction of thecells described in this invention and consists essentially of a seriesof two or more cells having one or more common electrodes wherein twoanode compartments served by opposite faces of the same anode alternatewith two cathode compartments served by opposite faces of the samecathode.

Variations of these figures utilizing fuel or gas membrane electrodes inplace of fuel-electrode can be made in accordance with the principlesdescribed above and need not be drawn here in detail.

Further, in any of the cells described containing a fuel or gaselectrode a suitable gas membrane electrode may sometimes be substitutedto advantage in accordance with the principles described above.

The invention may be better understood by reference to the followingdescription taken in connection with the drawings which are diagrammaticillustrations of the membrane-fuel cells within the scope of the presentinvention.

The cell of FIGURE 1 is an ordinary electrolysis cell in which at leastone fuel or gas membrane electrode is used in lieu of a conventionalelectrode to reduce part of the energy requirements. The elements ofthis cell are self explanatory from the drawing.

The cell of FIGURE 2 comprises an anode compartment 1 containing theelectrolyte solution 3 which is introduced into the compartment throughinlet 5 and is withdrawn by means of outlet 7, and anode 9 which iscomposed of a porous conductor capable of activating a combustible fuel,e.g., hydrogen gas, the anode functioning as an agent for absorbing andreleasing into the electrolyte solution in an electro-chemically activeform the combustible fuel, e.'g., a hydrogen-containing gas which entersthe electrode by means of inlet pipe 11 which extends into well 13 ofthe anode, said well being confined to the central portion of the anode.The cathode compartment 15 is separated from the anode compartment byion-exchange membrane 17 and contains an electrolytic solution 19 whichenters the compartment through inlet 21 and leaves through outlet 23 anda cathode 25 which is composed of a porous conductor capable ofactivating an oxidant fuel, e.g., oxygen gas, the cathode functioning toabsorb and release into the catholyte 19 in an electromechically activeform the oxidant, e.g., an oxygen-containing gas which enters thecathode by means of inlet 27. Inlet 27 extends into well 29 of theelectrode, said well being confined to the central portion of saidelectrode. Valves 31 and 33 located in inlets 11 and 27, respectively,serve to regulate the flow of combustible and oxidant gases, e.g. ofhydrogen containing and oxygen-containing gases, respectively, or toallow the use of but one fuel electrode when desired.

The operation of the cell of FIGURE 2, wherein the separatingion-exchange membnane is cation selected in character, may beillustrated as follows:

An aqueous solution of the electrolyte, for example, sodium chloride, isintroduced into the anode compartment 1 through inlet 5 and either wateror a dilute aqueous solution of an alkali metal hydroxide is passed intothe cathode compartment 15 through inlet 21. A hydrogen-containing gasin conducted into the anolyte sodium chloride 3, via the porous anode 9,an oxygen-containing gas is conducted into the catholyte 19 via theporous cathode 25 and a minimal amount of electric current (which sourceis not shown) is impressed upon the cell through electrodes 25 and 9.Hydrogen ions formed at the anode by the interaction of hydrogen gaswith the sodium chloride solution in conjunction with the chloride ionsof the electrolyte forms the corresponding acid, i.e. hydrchloric acid,which is withdrawn through exit 7. The cation Na+ is attracted towardthe cathode 25 and passes through the cation selective membrane 17,which allows its passage but repels the anionic chloride ions, into thecathode compartment 15 where it combines with hydroxyl 8 ions formed bythe interaction of oxygen with the catholyte 19 to form thecorresponding metal hydroxide, i.e. sodium hydroxide, which is withdrawnthrough exit 23.

The electrolytic cell of FIGURE 2 may be operated with oneanion-exchange membrane, in which instance, the electrolyte feedsolution is for example, introduced into the cathode compartment, theanionic group migrating to the anode to form the corresponding acid.These general procedures may also be run employing one gascontainingelectrode and one electrode of conventional design and function. It isapparent that in operations where the anode used is a conventional one,the anode compartment product would, in the case of a sodium chloridefeed solution, be chlorine gas, and in operations utilizing aconventional cathode, the cathode compartment product would be, forexample, hydrogen gas and/ or a metal such as Cu, Zn, Cd, etc.

It is evident that this procedure can be employed in the conversion ofsalts into their corresponding acids and bases. It may also beadvantageously applied to the purification of bases where the impurityis of an anionic nature, such as chlorine ions, or to the purificationof acids where the impurity is of a cationic nature, such as sodiumions. The mechanisms of these alternative applications will correspondto those underlying the interactions involving salts.

Among the further variations possible in the construction or applicationof the electrolytic cell employed in the general procedure are, forexample:

(1) A cell with a gas fed cathode and the anode is of conventionaldesign and function; (2) a cell with a gas fed anode and the cathode isof conventional design and function; (3) a three compartment cellwherein the electrolyte feed solution is electrochemically modified inthe center compartment between two ion exchange membranes; (4) a seriesof cell compartments with common electrodes wherein two anodecompartments served by opposite faces of the same anode, alternate withtwo cathode compartments served by opposite faces of the same cathode,the end compartments being an exception to such alternation.

In FIGURE 3 a three or more compartment electrolytic cell is defined byspaced permselective membranes 2 and 4, anode chamber 6 containing theporous anode electrode 8, having gas inlet 1i), extending into well 12of said electrode and said inlet having regulating valve 14 therein. Theporous cathode electrode 16 is located in cathode chamber 18 with inlet21) extending into well 22 of said electrode. The inlet 20 has aregulating valve 24 therein. All three chambers are provided with inlets26, 28, and 3t), and outlets 32, 34, 38, respectively for the flow ofelectrolytic solutions. The center compartment is desig nated at 46.

The operation of the cell of FIGURE 3 may be illustrated with respect toa process involving two or more ion-exchange membranes selectivelypermeable toward anions. Accordingly, an aqueous solution of theelectrolyte, for example, sodium sulfate is introduced into the centercompartment through inlet 28 while simultaneously there is introducedinto the anode compartment 6 Water at a rate determined by the :finalconcentration of the anode product desired. Into the cathode compartment18 water or a dilute aqueous solution of an alkali metal hydroxide ispassed. A hydrogen-containing gas, for example methane, is passed intothe anolyte 42 through inlet N and porous anode 8 and anoxygen-containing gas, for example air, is passed into the catholyte 44through inlet Ztl and porous cathode 16, while a minimal D.C. voltage isimpressed upon the cell. Ion-exchange membrane 4 permits the passage ofthe anionic group of the electrolyte feed in the center compartment,i.e. sulfate ions, toward the anode 8 where combination with hydrogenions formed by the interaction of hydrogen gas with the anolyte producesthe corresponding acid, i.e. sulfuric acid. The depletion of theoriginal electrolyte solution 40 in feed center chamber 46 of itsanionic groups, for example, sulfate ions, is compensated for by theconcurrent flow of hydroxyl ions from the cathode compartment throughmembrane 2 into the center compartment 46 where combination with thecation, sodium ions, produces the corresponding sodium hydroxide. Theefliuent from the cathode compartment is the dilute alkali metalhydroxide solution which has been regenerated by the production ofhydroxyl ions through an interaction at the cathode of oxygen with thecatholyte.

The processes of the above procedure can also be applied to cases wherethe original electrolyte is an impure acid whose impurities are of acationic nature, such as sodium ions, the purified acid being withdrawnfrom the anode compartment; and to cases where the original electrolyteis an impure base whose impurities are of an anionic nature, such aschloride ions, a purified base being withdrawn from the centercompartment.

The type of cell illustrated in FIGURE 3 may be set up in series,wherein two anode compartments served by opposite faces of the sameanode alternate with two cathode compartments served by opposite facesof the same cathode, which involves two or more alternating anion andcation permselective membranes.

In order to understand the operations of a third procedure, reference ismade to FIGURE 3 where membrane 4 is an ion-exchange membraneselectively permeable to anions and membrane 2 is an ion-exchangemembrane selectively permeable to cations. In this case, an aqueoussolution of the electrolyte, for example, sodium chloride solution, isintroduced into the center compartment through inlet 28, the centercompartment product being withdrawn through outlet 34. Simultaneouslywith the introduction of the sodium chloride solution, water isintroduced into the anode and cathode compartments through inlets 26 and30, respectively, or the water streams may be replaced by a diluteinorganic acid stream flowing into the anode compartment and a dilutealkali metal hydroxide solution into the cathode compartment. Acombustible liquid or gaseous fuel, e.g., a hydrogencontaining gas ispassed into the anolyte via the porous anode, a liquid or gaseousoxidant, e.g., an oxygen-containing gas is passed into the catholyte viathe porous cathode. If required, a minimal amount of additional DC.voltage from a conventional power supply is impressed upon the cell. Thecations, sodium ions, are attracted toward the cathode 16 and passthrough the cation permselective membrane 2 into the cathode compartment18 where they unite with hydroxyl ions formed from the interaction ofoxygen with the electrolyte therein to produce the correspondinghydroxide, sodium hydroxide. The anions, chloride ions, are attractedtoward the anode 8 and pass through the anion permselective membrane 4into the anode compartment 6 where they combine with hydrogen ionsformed from the interaction of hydrogen gas with the electrolyte thereinto produce the corresponding acid, hydrochloric acid. The anolyte andcatholyte eflluents may be recycled to their respective cellcompartments.

The cells of FIGURE 4 have center compartments designated by 51, 52, 53;anode compartments 54, 55, 56 and cathode compartments 57, 58 and 59.The fuelmembrane cathode electrodes are designated by 60 and 61 and areof the type previously described, and similarly constructed 62 and 63are the anodes similar in design and function to those of FIGURES l and2. Nos. 64, 65 and 66 are cation permselective membranes and 67, 68 and69, anion permselective membranes. Each compartment is equipped with aninlet and outlet for passage of electrolyte solutions. The inletmanifold for the oathode compartment is designated by 70, that for thecenter compartments by 71 and that for the anode compartments by 72. Theoutlet manifolds are designated as: catholyte 73, center 74 and anolyte75. The hydrogen-containing gas inlet manifold is 76 and theoxygen-containing 10 gas inlet manifold is 77. The electrodecompartments are defined by hydraulic and electric insulators 50 (suchas plastics, etc.) which also function to support said electrodes in thecompartments of the cell.

These cells may, however, contain only one ion-exchange membrane percell, in which case there are only two cell compartments per cell. Themembrane employed may be selectively permeable to either cations oranions.

The center compartment eflluent consisting of an electrolytic solutionis substantially depleted of both its cationic and anionic constituentsand is hence a relatively highly purified water product; therefore, thisgeneral procedure herein described serves as an eflicient and economicalmeans for purifying water of inorganic impurities and may be applicable,for example, in the purification of brackish water and seat water.Inversely, by reversing the position of the cation and anion membranes(or of the two electrodes) and feeding, for example, salt, to the endcompartments, the center solution may be concentrated which is, forexample, of interest in the production of salt from sea water. In thecase of commercial application of this general procedure toward eitherdesalting or the concentration of salt-containing water, the cell ispreferably equipped with a series of ion-exchange membranes, alternatingbetween those selectively permeable to cations and those selectivelypermeable to anions and numbering preferably from about ten to twentysuch pairs, thus separating the electrolytic cell into a series ofcompartments. In this particular system, the solution to bedemineralized is passed as the influent into alternating compartments,including the compartments containing the anode and cathode, the othercompartments serving to contain the flow of electrolyte-enriched(concentrated) water, that is, the concentrated streams alternate withthe demineralized water streams. In this manner, a relatively largevolume of water can be demineralized and/ or concentrated at low powerconsumption and at a relatively high rate.

This type of cell may be operated with only one gascontaining electrodeor it may be set up in series having common electrodes as was describedfor the first and second general procedures.

When porous cathodes and anodes are used in such concentration-dilutioncells, it is important to limit the number of cells intervening betweenthe fuel or gas electrodes so that the internal resistance is low enoughto per mit a reasonable current to pass therethrough. For example, inthe case of diluting and concentrating sea water in cells with membranesbetween 0.1 and 0.7 mm. thick and spaced between /2 and 2 mm. apart, thenumber of cell pairs between fuel or gas electrodes should preferablynot exceed about twenty.

T 0 demonstrate the energy advantage to be gained from the use of fuelelectrodes in appropriate electrolytes at practical current densities,the following series of experiments were carried out:

A simple electrolytic cell was constructed with two graphite electrodesof approximately 20 cm. electrode area. The aqueous electrolyte solutionused in this cell was (a) 20% KOH, (b) 20% NaOH, (c) 20% HCl. Thesesolutions were electrolyzed by impressing a DC. voltage across the twoelectrodes, utilizing a conventional DC. power supply. The voltagescorresponding to current density of 10 and milliarnperes/cm. weremeasured at a temperature of 30 C. and 60 C. The meas ured values arecontrol values referred to in Table I under the heading ConventionalElectrolysis.

In one series of fuel electrode measurements, the electrolysis wasrepeated after one of the conventional graphite electrodes, namely thecathode, was replaced with an oxygen fuel cathode of the same surfacearea (apparent). A porous carbon electrode comprising a silver oxidecatalyst is suitable. Oxygen gas was supplied to the fuel electrode inamount adequate to insure a slight excess of oxy- 1 1 gen. Table I showsthe voltage reduction obtained when an oxygen fuel electrode is used in20% KOH, 20% NaOH and 20% HCl, respectively, at current densities of 10and 100 milliamperes/cm Table I also shows that the oxygen cathode ismost effective in KOH, almost as good in NaOI-I with a significantlysmaller benefit in HCl.

In another series of experiments the same cell was used with aconventional graphite cathode but with a hydrogen anode. Againsufiicient hydrogen gas was supplied to insure an excess of hydrogen. Aporous graphite anode with a platinum catalyst is suitable. Table IIshows the results obtained employing a hydrogen anode, in potassiumhydroxide and in sulfuric acid.

It is seen that the hydrogen anode is quite elfective in both acids andbase, but clearly better in acid.

In still another series of experiments, the electrolysis was repeatedinserting in the cell a cation exchange membrane of the sulfonic typeutilizing as catl iolyte a 5 solution of NaOH and as anolyte a 20%solution of NaCl in order to compare the operation of this cell with aconventional steel cathode and an oxygen cathode. Table Ill shows thecomparative advantages of power savings (reduction in required voltage)in the use of the oxygen cathode over that of conventional electrolysis(non-fuel electrodes) TABLE I Oxygen Cathodes in Base and Acid CurrentConvcn- Oxygen Temp, 0. Density, Electrolyte tional Cathode,

Ina/cm. Eleetroly- Volts sis, Volts 10 20% KOH 1. 95 0. 100 20% KOH 2.4 1. 2 10 20% KO 1. 8 0.5 100 20% KO 2. 2 0. 9 10 20% NaOH... 1. 95 0. 8100 20% N20 1 2. 55 1.1 10 20% NaOH 1. 8 0. 6 100 20% NaOII- 2. 2 1. 210 20% HCL.- 1. 7 1. 4 100 20% HOL 2.1 2. 0 10 20% HCl 1.6 1.3 100 20%HCl 2.0 1.7

TABLE II Hydrogen Anode in Base and Acid Current Conven- Hydrogen Temp.,Density, Electrolyte tional Anode,

C. maJcm. Eloctroly- Volts sis, Volts 10 20% KOH 1. 95 0.6 100 20% KOII.2. 4 1. KOH. 1. 8 0. 4 100 20% KOH 2. 2 1. 2 1O H2804 1.225 sp. g 2. 20.8 100 HzSOi 1.225 sp. g 2. 9 1. 4 10 H 804 1.225 sp. g 1. 8 0.5 100H2504 1.225 Sp. g 2. 6 1.1

TABLE HI Oxygen Cathode in Caustic-Chlorine Cell Electrolyte Conven-Temp., Current tional Oxygen /O. Density, Electrol- Cathode,

ma./cm. Anolyte Catholyte ysis, Volts Volts 10 20% NaCl 5% NnOII 2.6 1.45 100 20% NaOl 5% NaOl-I 3. 7 2. 75 10 20% NaCl--. 5% NaO1-I 2. 0 0.9100 20% NaOl.-. 5",, NaOH..- 3. 3 2. 2

In general when a fuel membrane electrode is used in place of aconventional electrode, the same etfect is observed as above except thatthe internal resistance per unit thickness of electrolyte between theelectrodes is usually higher for the membrane electrolyte than it is forconcentrated electrolytes in solution. The high internal 12 resistancesignifies a higher voltage requirement corresponding to a given currentdensity.

In addition, the use of fuel membrane electrodes and/ or fuel electrodesin conjunction with membrane-defined chambers in a chemical conversioncell effects the improvements set forth hereinbefore, e.g., flexibilityin selecting the electrolyte most suited for the particular electrodeand subjecting other electrolytes in the other compartments of the cellto electrolysis or electrodialysis without contamination of either theelectrode or the solution to be converted; the membrane in contact withthe electrode protects the same against capillary sorption of theelectrolyte solution and against ionic impurities; separates the streamsor electrolytes which are necessary for chemical conversion; increasesthe eificiency of the product production of the fuel cell, etc.

The following examples are illustrative of the practice of the inventionand are not for purpose of limitation:

EXAMPLE 1 An electrolytic cell of the design represented by FIG- URE 2is constructed containing two graphite electrodes of approximately 20cm. area each, as flat plates, and the cation exchange membrane, forexample, of the styrene sulfonic acid type, is as described in US.Patent 2,731,411. The anode compartment of this cell is filled with anaqueous solution of sodium chloride (20%) and the cathode compartment isfilled with a 5% aqueous solution of sodium hydroxide. D.C. current isthen passed through this cell by applying to it a D.C. voltage from aconventional power supply. The voltages corresponding to 10 and 100rnilliamps/cm. at 30 C. and 60 C. are recorded in Table III as controls.The conventional graphite cathode is then replaced with an oxygenelectrode such as the one referred to above and used in 5% NaOH. Currentdensities of ten to 100 milliamps/cm. are passed and the correspondingvoltages are recorded in Table III.

It is clearly seen from the data of Table III above that caustic andchlorine are produced in this cell at a considerable saving in voltage,and consequently, power, when using oxygen cathode.

EXAMPLE 2 An electrolytic cell of the design represented by FIG- URE 2is constructed containing an ion-exchange membrane selectively permeableto cations, a porous graphite anode of rectangular shape having athickness of 1.0 inch, a porosity of 75% and an air permeability of 60cubic inches/sq. inch/minute/ atmosphere and which had previously beencoated with a thin coating of paraffin in order to render itwater-repellent, and a porous waterrepellent graphite cathode ofrectangular shape having a thickness of 2.0 inch, a porosity of 75% andan air permeability of 70 cubic inches/ sq. inch/minute/atmosphere. Thewalls of the cell are of Plexiglas. The membrane is composed of acopolymer of divinyl benzene and acrylic acid, and has a Water contentof 25%, an ion exchange capacity of 5.2 milliequivalents per dry gramand a specific resistivity of 25 ohm centimeters. The area of eachelectrode and membrane is 30 square centimeters.

A 5.3 N aqueous solution of sodium chloride having a temperature ofabout C. is conducted into the anode compartment at a rate adjusted sothat the corresponding effluent outflow is 1.5 ml. per minute. Water isconducted into the cathode compartment at a rate so that the effiuentoutflow therein is 0.28 ml. per minute. A current density ofmilliamps/cm. is maintained at the cathode by passing a direct electriccurrent of 3 amperes and 1.5 volts through the cell. A stream of 70%pure oxygen is passed into the porous cathode at a rate sufficient tosupply a slight excess at atmospheric pressure, and a stream of 90% purehydrogen is passed into the anode at a rate sufiicient to supply aslight excess at atmospheric pressure. The anolyte emuent consists of1.1 N hydro- 13 chloric and 4.2 N sodium chloride. The catholyteeffiuent consists of 5.9 N sodium hydroxide.

The flow of gases into the electrodes was discontinued to simulateconventional electrodes. The voltage required now is 4.3 volts,representing a savings of 2.8 volts by the use of gas electrodes and acorresponding saving in power consumption.

EXAMPLE 3 The procedure for example 2 is repeated, however, no hydrogenis admitted to the anode. The anode compartment product in this case ischlorine gas which analyzes to a purity of 98.9% after drying andliquefying. The savings in voltage and power realized in Example 1 arerepeated here.

EXAMPLE 4 An electrolytic cell of the design represented by FIG- URE 3is constructed containing two ion-exchange membranes selectivelypermeable to anions and two gas-activating electrodes described inExample 2. The membranes are composed of a copolyrner of styrene anddiviny'l benzene and contain 45% by weight of water which copolymer hasbeen chloromethylated and treated with trimethylamine (U.S. Patent No.2,780,604) have anion exchange capacity of 2.4 milliequivalents per drygram and a specific resistivity of 20 ohm centimeters. Each electrodeand membrane have an area equal to 40 cm.

An aqueous solution having a temperature of about 60 C. and consistingof 1.0 N sulfuric acid and 1.45 N ferrous sulfate is conducted into thecenter compartment at a rate adjusted so that the corresponding efiiuentflows out at a rate of 1.9 per minute. The anode compartment is fed withWater at about 60 C. so that the rate of flow of efliuent is 1.9 cc. perminute. The cathode compartment is fed with an aqueous solution of 1.0 NNaOH at a temperature of about 60 C. which is recirculated at a rate of50 ml. per minute. A current density of 100 amperes per sq. foot ismaintained at the cathode by passing a direct electric current of 4.0amperes and 1.4 volts through the cell. A stream of 96% pure oxygen ispassed into the cathode at a rate suiiicient to supply a slight excessat atmospheric pressure and a stream of 90% pure hydrogen is passed intothe anode at a rate sufficient to supply a slight excess at atmosphericpressure. The anolyte efliuent consists of 1.0 N sulfuric acid and thecenter compartment eflluent consists of 1.45 N ferrous sulfate.

The flow of gases into the electrodes was discontinued. The voltagerequired now is 4.6. The use of gas-containing electrodes represents asavings of 3.2 volts over a similar process utilizing conventionalelectrodes and consequently represents a corresponding savings in powerconsumption.

EXAMPLE 5 An electrolytic cell of the design represented by FIG- URE 3is constructed containing one ion-exchange membrane selectivelypermeable to cations and another selectively permeab le to anion. Thecation permselective membrane is similar to that used in Example 1, theanion pe-rmselective membrane similar to those used in Example 4.

A 5.3 N aqueous solution of sodium chloride is conducted into the centercompartment and recirculated through this compartment at a rate of ml.per minute. The anode compartment is fed with water so that the effluentoutflow is 0.64 ml. per minute. The cathode compartment is fed with'water so that the efiiuent outflow is 0.64 ml. per minute. Thetemperature of the efiiuents are approximately 60 C.

A current density of 100 amperes per square foot is maintained at thecathode by passing a direct electric current of 3 amperes and 1.8 voltsthrough the cell. A stream of 96% pure oxygen is passed into the cathodeat an adequate rate at atmospheric pressure and a stream of 90% purehydrogen is passed into the anode at an adequate rate at atmosphericpressure. The anolyte effluent consists of 3 hydrochloric acid and thecatholyte eflluent consists of 3 N sodium hydroxide.

The flow of gases into the electrodes was discontinued. The voltagerequired now is 4.8. The use of gas-containing electrodes thereforerepresents a savings of 3.0 volts over a similar process utilizingconventional electrodes and consequently represents a correspondingsavings in power consumption.

EXAIMPLE 6 An electrolytic cell of the design represented by FIG- URE 4is constructed containing three cation permselective membranes similarto that used in Example 1 and three anion permselective membranessimilar to those used in Example 4. The cell has two poroushydrogenactivating anodes and two porous oxygen activating cathodessimilar to those used in Example 5. The construction of the cell is suchthat there are three cell pairs wherein the order of electrodes andmembranes are as follows: cathodecation membrane-anionmembraneanodeanion membrane-cation membrane-cathode cationmembrane-anion membrane-anode.

The cell is now operated in a manner similar to that employed in Example5 using similar solutions, similar eiiluent rates and similar electricalconstants. The effiuent solutions have similar concentrations. The totalcurrent density is 93 amperes per square foot and the voltage is 1.8volts.

The flow of gases into the electrodes was discontinued. The voltagerequired now is 4.8 volts, representing a savings of 3.0 volts and acorresponding savings in power consumption when gas electrodes wereemployed.

EXAMPLE 7 An electrolytic cell assembly consisting of the cells of thegeneral design represented by FIGURE 3, is constructed containing tenion-exchange membranes selec tively permeable to cations andion-exchange membranes selectively permeable to anions in alternatingorder. The cell, as set up, contains 19 center compartments and two endcompartments. The latter are functionally equivalent to the centercompartments, since the electrodes in these end compartments are boundedby membranes. Ten of the center compartments in alternating order serveas concentrating chambers and 9 of the center compartments and the twoend compartments, serve as diluting or feed chambers.

Into the feed chambers is introduced at a rate of about 18 ml. perminute and at a temperature of about 50 C. a 0.6 N aqueous sodiumchloride solution. Into the concentrating chambers is introduced Waterat the same rate and temperature.

A current density of 45 milliamperes/cm. is maintained at the cathode bypassing a direct electric current of 1.3 amperes and 1.2 volts throughthe cell. A stream of 96% pure oxygen is passed into the cathode atatmospheric pressure and a stream of pure hydrogen is passed into theanode at atmospheric pressure, both gases at rates slightly in excess ofthe rate of H 0 formation.

The total flow per cell assembly is 38 ml. per minute; the totalconcentrating chamber eflluent flow is 23 ml. per minute and consists ofa 0.8 N sodium chloride solution; the total diluting chamber effluentflow is 15 ml. per minute and consists of a 0.3 N sodium chloridesolution.

The flow of gases into the electrodes was discontinued. The voltagerequired now is 5.5 volts representing a savings of 4.3 volts and acorresponding savings in power consumption when employing gaselectrodes.

EXAMPLE 8 An electrolytic cell of the design represented by FIG- URE lis constructed containing a hydrogen-cation exchange membrane anode, asolution of electrolyte containing 250 g. per liter ofchromium-trioxide, CrO and 2 /2 g./liter of sulfuric acid. The cathodeconsists of a piece of iron to be chromium plated. A current density of5075 milliamps/cm. is passed through this cell at a voltage of between 2/2 and 3 volts instead of the usual 5-6 volts which were required whenordinary lead anodes were used in place of the hydrogen membraneelectrode. In this example the cation membrane prevents the access ofchromic acid to the anode thereby avoiding the un desirable reduction ofthe chromic acid.

Having now described typical examples of cell operation according tothis invention, it will sufiice to list more significant examples ofindustrial applications wherein this principle can be utilized.

EXAMPLE 9 An electrolytic cell of the design of Example 5 is constructedhaving three compartments formed by two electrodes and one cationselective membrane and one anion selective membrane, the cation membranebeing a carboxylic type near the cathode, and the anion membrane being aweekly basic high capacity type near the anode.

A 3.2 N solution of sodium sulfate is fed to the center compartment andrecirculated at 8 ml. per minute. The anode compartment is fed withwater or 4.8 sodium sulfate at a rate such that the effluent outflow is0.71 ml. per minute. The cathode compartment is fed with water so thatthe efflucnt outflow is 0.71 mL/min. The temperature of the eflluents isabout 40 C.

A current density of 200 milliamps per square cm. is maintained at thecathode by passing a direct current of 6 amperes at 2.1 volts throughthe cell. A stream of 90% pure oxygen is passed into the cathode at anadequate rate at atmospheric pressure, and a stream of water gas(approximately 45% methane and 45% H is passed into the anode at anadequate rate at atmospheric pressure. The anolyte consists of 4.8 N H80 or 4.8 N NaHSO and the catholyte efiiuent consists of 2.4 N sodiumhydroxide.

The flow of gases to the electrodes is stopped and the voltage nowrequired to pass current at the same current density is 4.8 volts.

EXAMPLE 10 An electrolytic cell of the design of FIGURE 1 is constructedcontaining a hydrogen-cation exchange membrane anode, a copper cathode,an electrolyte solution consisting of leach liquor from low grade copperores with about 36 grams per liter of copper (as copper sulfate) and 40grams per liter of sulfuric acid. A current density of 10 milliamps persquare cm. is maintained at the cathode by impressing a voltage of about0.5 volt across the cell. Ninety percent pure hydrogen is passed intothe anode at an adequate rate. Greater than 99 percent pure copper isdeposited at the cathode. When the hydrogen gas flow into the anode isstopped, the potential across the cell has to be increased to about 2.1volts to maintain the current density thus illustrating the savings inpower gained through use of this invention.

The advantages gained in power saving in the electrowinning of copperalso apply to a corresponding degree in the electrowinning of Ni, Cr,Cd, Pb, Zn, Ag, Sn, Mn, Sb, Co and Fe, as will be apparent from thefollowing three further examples directed to chromium, cobalt, andcadmium.

EXAMPLE 11 An electrolytic cell of the design of FIGURE 1 is constructedcontaining a hydrogen-cation fuel membrane anode, and an aluminum bronzecathode for the electrowinning of chromium. The electrolyte is preparedfrom ammonium chrome alum from the sulfuric acid leach of low gradechromium ores and contains approximately 90 grams per liter chromium andgrams per liter ammonia. Hydrogen gas is passed into the anode and acurrent density of 70 milliamps per square cm. is maintained at thecathode with a cell potential of 3.1 volts at an operating temperatureof 46 C. When an inert conventional anode electrode such as lead wasused in place of the fuel cation membrane anode the cell potential hadto be increased to 4.3 volts, thus illustrating the savings in power.

EXAMPLE 12 A cell of the design of FIGURE 1 is constructed with ahydrogen fuel cation membrane anode and a stainless steel cathode forthe electrowinning of cobalt. The electrolyte consists of a solution of20 grams per liter cobalt as cobalt sulfate, 50 grams per liter boricacid, and 5 grams per liter sodium fluoride. The cell is maintained at60 C. Hydrogen is passed into the anode and a current density of 25milliamps per square cm. is applied to the cathode at 1.2 volts. Greaterthan 99 percent pure cobalt is deposited at the cathode. Where the cellwas operating with an inert or conventional anode such as lead,increased power was required as shown by the operating cell voltage of2.8 volts.

EXAMPLE 13 In order to demonstrate the electrowinning of cadmium, a cellis constructed of the design of the previous example with an aluminumcathode. When hydrogen is passed into the anode and the cell is operatedat a current density of 10 milliamps per square cm. at 1.5 volts,cadmium is deposited as the cathode from an electrolyte containing 180grams per liter cadmium and grains per liter sulfuric acid. On operatingthe cell with an inert anode, such as lead, the voltage necessary wasincreased to 2.8 volts.

EXAMPLE 14:

An electrolytic cell corresponding to FIGURE 1 is constructed with acation membrane anode and a cathode consisting of a mold of a piece tobe electroformed. The electrolyte consists of CuSO 255 grams per liter,and sulfuric acid, 75 grams per liter. A current density of 200milliamps per square cm. is maintained at the mold cathode at 1.1 volts.Methane gas is introduced into the anode. A conventional electroformingcell operating at this current density requires a voltage of 2.5 voltsthus illustrating the power savings of this invention.

EXAMPLE 15 A cell of the design of FIGURE 1 is constructed with ahydrogen cation membrane anode, an iron cathode to be electrogalvanizedand an electrolyte of 200 grams of Zn per liter and 250 grams of H perliter. The current density at the cathode is 1 amp per square cm. andthe voltage across the cell is 2.5 volts. percent pure hydrogen ispassed into the anode at an adequate rate. Hydrogen gas liberated at thecathode is collected and recirculated to the anode to supply part of thefuel. In the absence of the fuel membrane anode 4 volts is required tomaintain the current density thus demonstrating the savings accomplishedby the process of this invention.

EXAMPLE 16 A cell of the design of FIGURE 2 is constructed with porousgas electrodes at both anode and cathode with a cation membraneseparating anolyte and catholyte. Spent pickle liquor consisting of 1 NH 80 and 2 N FeSO is fed into the anode compartment and 1 N NaOH isrecirculated in the cathode compartment. A current density ofmilliamperes per square cm. is maintained at the electrode by passing acurrent of 3.0 amperes at 1 volt through the cell. 70 percent pureoxygen is passed into the cathode and 90 percent pure hydrogen into theanode at an adequate rate. The anolyte effluent outflow is 1.2 ml. perminute at a composition of 2.5 N H 50 and 0.5 N FeSO In the regenerationof spent pickle liquor without fuel electrodes, the voltage drop acrossthe cell is 3.5 volts thus illustrating the saving in voltage andconsequently of power in the process.

EXAMPLE 17 The electrolytic cell of the previous example is replacedwith an inert cathode and the cell is otherwise operated in the samemanner with spent pickle liquor. Hydrogen gas evolved at the cathode inthe electrolysis is circulated to the porous hydrogen anode thussupplying part of the hydrogen requirement. In this case, the voltageacross the cell is 2 volts with a saving of 1.5 volts over the cellhaving both electrodes of inert material.

EXAMPLE 18 A cell of the design of FIGURE 2 is constructed of Monel witha screen diaphragm on the anode side of the cation membrane. The anodeis constructed of nickel and the cathode is a porous oxygen electrode.The catholyte consists of 1 N potassium hydroxide and is re circulatedat 50 ml. per minute. The anolyte is KF-3HF and is recirculated at 50ml. per minute. The cell is operated at 55 C. with a current density of70 ma. per square cm. at the anode and an operating voltage of 7.1volts. 70 percent pure oxygen is fed into the porous cathode at anadequate rate and 98% pure fluorine is generated at the anode. With aMonel cathode as in the conventional fluorine cell, the operatingvoltage is 8.4 volts compared to the use of 7.1 volts noted above.

EXAMPLE 19 A cell of the design of FIGURE 2 is constructed with a porousoxygen cathode, a graphite anode and a cation membrane separating anodeand cathode compartments. A 1.0 N sodium hydroxide solution iscirculated in the cathode compartment and an electrolyte containingsaturated sodium chloride and 1.3 grams per liter HCl is recirculated inthe anode compartment. A current density of 30 milliamps per square cm.is passed to the anode at 2.5 volts. 70 percent pure oxygen is passedinto the cathode at an adequate rate. Sodium chlorate is produced in theanode compartment at lower voltages than in the conventional cell, 3.6v., and at a higher current efiiciency due to elimination of thereduction of ClO at the cathode due to the presence of the ion exchangemembrane in the cell.

I claim:

1. An electrolysis cell comprising: a container, a cathode, and a spacedporous catalytic anode therein, a cation exchange membrane between andseparating said electrodes, said membrane being spaced from at leastsaid cathode electrode, means for passing a combustible fuel into saidporous catalytic anode electrode, and means for passing a directelectric current between said cathode and anode.

2. The cell of claim 1 wherein the porous catalytic anode is a porouscatalytic gas electrode.

3. The cell of claim 1 wherein the container comprises a single liquidelectrolyte compartment and said cation exchange membrane is inface-.to-face contact with said porous catalytic anode.

4. The cell of claim 1 wherein said ion-exchange membrane is a spacedbarrier defining two compartments between said electrodes.

5. A composite electrode comprising a porous catalytic electrode havingan ion-exchange membrane secured to and in face-to-face contact with theactive surface of only said electrode.

6. The composite electrode of claim 5 wherein said electrode is a porouscatalytic anode.

7. A process for electrolytic conversion of electrolyte solutions in anelectrolytic cell comprising: a container adapted to contain anelectrolyte solution, spaced electrodes therein at least the anode beinga porous catalytic electrode, a cation exchange membrane between saidelectrodes and spaced from the cathode electrode, comprising the stepsof: introducing an electrolyte solution into the 1% container, passing adirect electric current between said electrodes, and passing acombustible fuel through said porous anode to lower the energyrequirements for conversion of said electrolyte solution by the reactionof said combustible fuel.

8. The method of cathodically depositing a metal from an aqueouselectrolyte solution containing a salt of said metal, which comprisesintroducing said electrolyte into a cell containing a cathode and aspaced anode, the latter consisting of a porous catalytic electrode inface-to-face contact with a cation-exchange membrane, saidcationexchange membrane being in the hydrogen form, passing acombustible gas into said anode, passing a direct current through saidelectrolyte between the anode. and cathode, and collecting depositedmetal at said cathode.

9. The method or" claim 8 wherein the metal to be deposited is selectedfrom the group consisting'of Cu, Cd, Co, Fe, Ni, Cr, Pb, Ag, Sn, and Zn.

10. The method which comprises: passing a mixture of sulfuric acid andferrous sulfate into the anode compartment of a two compartment cellhaving electrodes therein separated by a selective cation-exchangemembrane defining said compartments into anode and cathode compartments,at least the anode being a porous catalytic electrode, maintaining anelectrolyte solution in said cathode compartment, passing .a combustiblegas into said porous catalytic anode electrode, passing a direct currenttransversely through said electrodes, membrane and electrolytes, andremoving a sulfuric acid bearing solution from the anode compartment.

11. The method of cathodically depositing a metal from an aqueouselectrolyte solution containing a salt of said metal, which comprisesintroducing said electrolyte into a cell containing a cathode and ananode, the latter consisting of a porous catalytic electrode, acationcxchange membrane between said electrodes and spaced from saidcathode, said cation-exchange membrane being in the hydrogen form,passing a combustible gas into said anode, passing a direct electriccurrent through said electrolyte between the anode and cathode,collecting deposited metal at said cathode, and removing the convertedelectrolyte from the cell.

12. The method of cathodically depositing a metal from an aqueouselectrolyte solution containing a salt of said metal, which comprisesintroducing said electrolyte into a cell containing a cathode and ananode, the latter consisting of a porous catalytic electrode infaceto-face contact with a cation-exchange membrane between saidelectrodes and spaced from said cathode, said cation-exchange membranebeing in the hydrogen form, passing a combustible gas into said anode,passing a direct electric current through said electrolyte between theanode and cathode, collecting deposited metal at said cathode andremoving the converted electrolyte from the cell.

References Cited in the file of this patent UNITED STATES PATENTS1,182,759 Emanuel May 9, 1916 1,954,664 Cain Apr. 10, 1934 2,273,036Heise et al. Feb. 17, 1942 2,273,796 Heise et al. Feb. 17, 19422,358,419 Schumacher et al. Sept. 19, 1944 2,390,591 Janes Dec. 11, 19452,700,063 Manecke Jan. 18, 1955 2,810,686 Bodamer et a1 Oct. 22, 1957FOREIGN PATENTS 400,787 France Aug. 7, 1909. 213,404 Australia Feb. 26,1958 213,405 Australia Feb. -27, 1958 794,471 Great Britain May 7, 1958

7. A PROCESS FOR ELECTROLYTIC CONVERSION OF ELECTROLYTE SOLUTIONS IN ANELECROLYTIC CELL COMPRISING: A CONTAINER ADAPTED TO CONTAIN ANELECTROLYTE SOLUTION, SPACED ELECTRODES THEREIN AT LEAST THE ANODE BEINGA POROUS CATALYTIC ELECTRODE, A CATION EXCHANGE MEMBRANE BETWEEN SAIDELECTRODES AND SPACED FROM THE CATHODE ELECTRODE, COMPRISING THE STEPSOF: INTRODUCING AN ELECTROLYTE SOLUTION INTO THE CONTAINER, PASSING ADIRECT ELECTRIC CURRENT BETWEEN SAID ELECTRODES, AND PASSING ACOMBUSTIBLE FUEL THROUGH SAID POROUS ANODE TO LOWER THE ENERGYREQUIREMENTS FOR CONVERSION OF SAID ELECTROLYTE SOLUTION BY THE REACTIONOF SAID COMBUSTIBLE FUEL.